Plasma and peritoneal fluid concentrations of ceftriaxone after intravenous and intraperitoneal administration in horses

•Ceftriaxone was administered to horses by the intraperitoneal (IP) and intravenous (IV) routes.•Plasma and peritoneal fluid concentrations of ceftriaxone after IP and IV administration were compared.•IP administration of ceftriaxone resulted in higher peritoneal fluid concentrations than IV administration.•After IV administration, plasma ceftriaxone had a minimal inhibitory concentration (MIC)>1μg/mL for 12h.•After IP administration, plasma ceftriaxone had a MIC>1μg/mL for 24h. Intraperitoneal (IP) use of antimicrobial agents may lead to therapeutic effects with better clinical results than intravenous (IV) administration. The aim of this study was to compare plasma and peritoneal fluid concentrations of ceftriaxone after IP and IV administration in horses, and to evaluate possible adverse effects. One group of five horses received 25mg/kg ceftriaxone diluted in 1L saline solution by IP catheter once daily for 5 days, while a second group of five horses received 25mg/kg ceftriaxone diluted in 250mL saline solution by IV injection once daily for 5days and 1L saline solution by IP catheter once daily for 5 days. Peritoneal fluid and plasma were collected to determine ceftriaxone concentrations after the first and fifth administration. IP administration of ceftriaxone resulted in concentrations above a minimum inhibitory concentration (MIC) of 1μg/mL for 24h in peritoneal fluid and for 12h in plasma, while IV administration of ceftriaxone resulted in lower peritoneal fluid concentrations, which remained above a MIC of 1μg/mL for 12h in peritoneal fluid and 10h in plasma. No adverse effects were observed. Comparisons of ceftriaxone concentrations, time of occurrence of the maximum (Tmax) and minimum (Tmin) concentrations, and the mean residence time (MRT), between the two groups showed that IP administration provided greater availability of cephalosporin in peritoneal fluid. The IP use of ceftriaxone (25mg/kg diluted in 1L saline solution once daily) may be useful for the prophylaxis and/or treatment of peritonitis in horses.